Viewing images of ivory is not harming an elephant, though. With CSAM, the image is the abuse – you'd be viewing the actual harm event. So consuming CSAM is more like purchasing the ivory yourself.
What incentives do people have to pay? Scarcity. Which, in the era when anyone willing can just generate any questionable imagery, is no longer that scarce.
The less resources are directed towards capturing people for having bad files on their PCs, the more resources are freed up for actively persecuting any commercial operations and doing the actual field work.
We could make it illegal to view images of ivory (with the logic that this might lead to a sale), but most people would consider that a step too far.